This is a prospective observational non-intervention study evaluating the dynamic CTC count during the chemotherapy. Patients provide written informed consent and pass the screening. Peripheral blood will be drawn before and after the first line chemotherapy. Analyze the relationship between CTC count and clinical outcome. The time points of blood drawing are set as following: once prior to 1st cycle of chemotherapy, once 1 week prior to 2nd cycle of chemotherapy, posterior to 4th cycle (or less than 4th cycle) of chemotherapy and once when progressive disease (PD). The specific blood tube CellSave Tube will be used, 7.5ml blood sample every time. One follow-up (including by phone) be made every 3 month after PD until death. The clinical outcome of first line chemotherapy will be ultimately obtained.